Chiari Malformations

1:1000 live births

Increased use of MRI leading to greater diagnosis

Chiari malformation types I and II: Most common pediatric hindbrain abnormality

Chiari type II always accompanied by myelomeningocele (which occurs in 0.6 of 1000 live births)

Respiratory and gastrointestinal dysfunction

OSA, which has been targeted as an independent risk factor in perioperative morbidity, regardless of type of procedure

Herniation

Increased ICP

Herniation

Hydrocephalus

Syringomyelia

Respiratory and cardiac center dysfunction

Neurogenic dysphagia

Rapid neuro deterioration in Chiari type II

Group of hindbrain abnormalities ranging from herniation of cerebellar tonsils to cerebellar agenesis

Often complicated by syringomyelia, a cavity fluid collection of the spinal cord

Classification of Chiari malformations: Types I to IV (also type 0 and 1.5):

• I: Herniation of cerebellar tonsils through foramen magnum into upper cervical spinal canal, disrupting normal CSF flow; not typically associated with hydrocephalus, but often complicated by syringomyelia (30–70%); referred to as adult-type secondary to delayed diagnosis

• II (Arnold-Chiari): Herniation of cerebellar vermis, brainstem, and fourth ventricle through foramen magnum in the setting of myelomeningocele; commonly associated with both syringomyelia (20–95%) and hydrocephalus (90%)

• III: Very rare, extreme malformation (<1%) in which cerebellum and brainstem herniate into posterior encephalocele; associated with poor prognosis, severe neurologic deficits, respiratory insufficiency, developmental delay, and hydrocephalus

• IV: Cerebellar hypoplasia or aplasia without associated herniation (extremely rare)

• 0: Syringomyelia without tonsillar herniation that resolves with posterior fossa decompression

• 1.5: Similar to type I but other brainstem components are herniated, in addition to cerebellar tonsils

No unifying pathophysiologic mechanism between different types

Multiple hypothesis to explain various malformations

Syringomyelia may have a common origin between different Chiari malformations related to altered CSF dynamics

Slightly more prevalent in female gender and European ethnicity